Drillable Debris Barrier Tool

ABSTRACT

A drillable debris barrier tool is positioned under a stage tool to protect tools therebelow from contamination with debris from the stage tool, as it is drilled out. The debris barrier tool includes features that facilitate drill up of stage tool debris and reduce the size of debris generated from removal of the barrier tool.

FIELD

The invention relates to a wellbore tool and method and, in particular,a barrier tool for wellbore string applications, wellbore strings andmethods.

BACKGROUND

A wellbore string, such as of casing or liner, but herein collectivelycalled casing, may be cemented into a well. When the string includestools, such as open hole completion tools, a stage tool may be employedto allow cement placement in the annulus above the tools.

In such a string installation, the casing is run into the well. Cementis then pumped down the casing, out the ports of the stage tool into theannulus surrounding the casing. In some embodiments, a wiper plug ispumped down the casing and is used to close the communication ports onthe stage tool. The wiper plug, if any, and internal components of thestage tool are then drilled out to provide an inside diameter throughwhich intervention tools and balls may pass. In order to prevent debrisfrom the drilled out stage tool falling down the hole, where it mayinterfere with the functioning of the string's tools, a barrier tool isused to catch debris. After drilling out the stage tool, the barriertool also has to be drilled out. Overall, the passage of fragmentsshould be avoided to avoid interference with the performance of thestring's tools down hole of the barrier tool. In addition, it isdesirable that the drill out process generate an inner diameter throughthe drilled out tool without jagged edges and with a diameter suitablefor tubing conveyed tools to pass.

SUMMARY OF THE INVENTION

In accordance with a broad aspect of the present invention, there isprovided a debris barrier tool comprising: a liner forming a seat in abore through the tool, the seat formed to retain a ball to be landed inthe seat, wherein the liner is formed of a cast iron.

In accordance with another broad aspect of the present invention, thereis provided a method for drilling out a wellbore string comprising:landing a ball in a seat of a debris barrier tool; operating a drillingassembly to drill through the wellbore string uphole of the debrisbarrier tool; and drilling through the seat of the debris barrier toolwhile debris from uphole drilling is crushed between the drillingassembly and the debris barrier tool.

It is to be understood that other aspects of the present invention willbecome readily apparent to those skilled in the art from the followingdetailed description, wherein various embodiments of the invention areshown and described by way of illustration. As will be realized, theinvention is capable for other and different embodiments and its severaldetails are capable of modification in various other respects, allwithout departing from the spirit and scope of the present invention.Accordingly the drawings and detailed description are to be regarded asillustrative in nature and not as restrictive.

DRAWINGS

A further, detailed, description of the invention, briefly describedabove, will follow by reference to the following drawings of specificembodiments of the invention. These drawings depict only typicalembodiments of the invention and are therefore not to be consideredlimiting of its scope. In the drawings:

FIGS. 1A, 1B, 1C, 1D, 1E and 1F are schematic sectional views through awellbore with a production casing installed therein. The FIGS. 1A, 1B,1C, 1D, 1E and 1F show the wellbore, respectively, after casing run in,just prior to cementing, during cementing, just after cementing, duringdrill out and after drill out.

FIGS. 2A, 2B, 2C and 2D are axial sectional views of a debris barriertool during installation, during cementing, during drill out and afterdrill out, respectively.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

The description that follows and the embodiments described therein areprovided by way of illustration of an example, or examples, ofparticular embodiments of the principles of various aspects of thepresent invention. These examples are provided for the purposes ofexplanation, and not of limitation, of those principles and of theinvention in its various aspects. In the description, similar parts aremarked throughout the specification and the drawings with the samerespective reference numerals. The drawings are not necessarily to scaleand in some instances proportions may have been exaggerated in ordermore clearly to depict certain features.

With reference to the Figures, a drillable debris barrier tool 10includes a tubular body suited to installation in a wellbore string 12.Tool 10 includes an outer tubular housing 14 and an inner liner 16.Outer tubular housing 14 has an open upper end 14 a and an open lowerend 14 b and a bore 14 c extending between the ends. In this embodiment,these ends 14 a, 14 b are formed, for example as by threading, forconnection into a string. Bore 14 c has an inner diameter ID that issubstantially a full bore diameter, which is within the nominal diameteracross bore 12 b of string 12 and greater than the drift diameter.

Inner liner 16 is positioned substantially concentrically within outerhousing 14. The inner liner is positioned in an annular recess 18 in thewall of the outer housing. The annular recess is spaced from the ends ofthe housing.

Inner liner 16 has a tubular form, wherein a bore 20 extends through theliner from its upper end 16 a to its lower end 16 b such that a fluidpassage is provided through the liner and the tool. The bore has definedtherein a seat 22 which is a constriction where the bore's diameter isreduced relative to other portions of the bore. The inner walls definingthe bore may be formed frustoconically, as at 22 a, leading to theconstriction forming seat 22. The seat accepts and retains a ball 24 orother plug form. The ball used with barrier tool 10 is sized to passthrough string uphole of tool 10 and to enter bore 20. However, the ballis selected to have a diameter too large to pass through the seat 22.Thus, ball 24 can be dropped to land in seat 22 of the barrier tool whenit is desired to plug bore 20.

The debris barrier tool may be used in a string 12 and in a wellboreinstallation, for example as shown in FIGS. 1A to 1F. Barrier tool 10may, for example, be used in conjunction with a stage tool 30 in acemented-in wellbore string application. String 12, which may beproduction casing or another form of liner, includes a stage tool 30 forstage cementing and tools down hole of the stage tool. The tools may becompletion tools such as packers 32, wellbore treatment tools 34, etc.In the illustrated embodiment, the wellbore treatment tools 34 areball-activated frac sleeves. However, barrier tool 10 may be employedwith other string configurations and tools such as, for example,screens, full bore frac sleeves or burst type tools.

Stage tool 30 allows stage cementing wherein cement C may be introducedto the annulus 11 between string 12 and the wellbore wall 13, hereinpartially defined by surface casing 13 a. A stage tool allows cement tobe introduced along a length of the string without the need to flow thecement out the distal end 12 a of the string, which is useful if thestring includes tools 32, 34 not conducive to placement of cementthereabout.

After stage tool 30 is used to stage cement, the stage tool is drilledout to open the string's bore 12 b to a drilled out diameter which islarge enough for wellbore structures moved through the bore to pass.Wellbore structures may include actuators, such as balls to actuatewellbore treatment tools 34, strings such as intervention strings, toolssuch as shifting tools, etc. The drilled out diameter is that diameterlarge enough for wellbore structures moved through the bore to pass and,as such, may sometimes be less than the drift diameter. However, thedrilled out diameter often is about the same as or greater than thedrift diameter. In some embodiments, the drilled out diameter may be atleast as large as (i.e. greater than or equal to) the drift diameter,but is generally less than or equal to the full bore diameter.

Barrier tool 10 is positioned in the string's bore 12 b between stagetool 30 and the string's tools 32, 34. That is, the barrier tool ispositioned in the string bore down hole of the stage tool and uphole ofthe string's tools. Thus, barrier tool 10 is positioned to protect tools32, 34 from debris generated by the drill out of stage tool 30.

In use, production casing 12 is run into the well 13 (FIG. 1A). This mayinclude running the string into a horizontal and/or open hole section13′ of the well. At the desired depth, packers 32 are set (FIG. 1B). Inone embodiment, packers may be hydraulically set to expand out andengage the wellbore wall. In the illustrated embodiment, packers 32 areof the type known as open hole and hydraulically set and pressure isapplied through string 12 to set the packers.

During this process, as shown in FIG. 2A, the barrier tool bore 20remains open so that fluid can be circulated therethrough and, thus,pressure can be communicated therebelow to packers 32.

The stage tool is also manipulated to open ports 30 a establishingcommunication between the inside bore 12 b of the casing string and theannulus 11. The stage tool can be manipulated to open by variousprocesses. In one embodiment, for example, the stage tool can also beactuated hydraulically to open ports 30 a. Depending on the operation ofstage tool, this may be conducted with the setting of packers, while thebarrier tool remains open or after the barrier tool is closed, describedbelow.

At least before cementing, ball 24 is circulated down the casing andlands on the drillable debris barrier tool 10 (FIGS. 1B and 2B). Thiscloses access through bore 12 b to the string and its components below(i.e. down hole of) tool 10. Cement C is then pumped down the casing(FIG. 1C), out the ports of the stage tool into the annulus surroundingthe casing. The cementing operation is then concluded and the stage toolis then closed. For example as shown in FIGS. 1C and 1D, a wiper plug 30b may be pumped down the casing to land on a stop 30 c in the stagetool. Wiper plug 30 b may be used to force the residual cement down tothe stage tool and to close communication ports 30 a on the stage tool.

The wiper plug 30 b and internal components such as stop 30 c of thestage tool are then drilled out by a drilling assembly 40 including amill to provide the drilled out diameter Ds through bore 12 b. Even ifsome remnants of stage tool 30 s remain, the drilled out diameter, asnoted, is large enough so that intervention string and tools and/orballs for tools 34 may pass (FIGS. 1E and 2C).

Barrier tool 10 acts during drill out to at least substantially preventstage tool debris 30 d from moving therepast and falling down the holewhere the debris may interfere with the functioning of tools 34. Forexample, the barrier tool with ball 24 therein provides a platform (FIG.2C) to catch the debris generated by drill out. Further, the barriertool provides a platform against which the debris can be drilled intosmall enough pieces that they can be circulated out of the well.Circulation may be through the drilling assembly 40 in the forwarddirection with fluid passing out of the drilling assembly and up theannular area between casing 12 and the drilling assembly 40.

At some point during or after the stage tool debris is drilled intosmall pieces, the components of the debris barrier tool that constrictthe inner diameter also have to be drilled out. As shown in FIG. 2D, thesurface of barrier tool 16 s remaining after an opening is drilledthrough the seat of the debris barrier tool should have a relativelysmooth surface, substantially without abrupt shoulders or jagged edgesand should have a drilled out diameter D large enough for wellborestructures moved through the bore to pass. As noted above, wellborestructures may include actuators, such as balls to actuate wellboretreatment tools 34, strings such as intervention strings, tools such asshifting tools, etc. While the drilled out diameter D may be less thanthe drift diameter, in some embodiments, the drilled out diameter may beat least as large as (i.e. greater than or equal to) the drift diameter,but is generally less than or equal to the full bore diameter. The drillout diameter is about the same or slightly larger than the diameter ofthe mill. Thus, if the same mill is used to drill out stage tool 30 andbarrier tool 10, the drilled out diameters Ds and D are substantiallythe same.

To protect the tools, the barrier tool seat in liner 16 and ball 24drill up substantially without generating large fragments and withcirculation such that fragments are deterred from falling down hole,thus avoiding interference of fragments with the performance of thetools 34.

After drill out, the string including at the location of stage tool 30and barrier tool 10 is opened up to the drilled out diameter. The stringcan then be used for wellbore treatments (FIG. 1F) such as fluidtreatments, arrows F, through tools 34.

The drillable debris barrier tool 10 includes a combination of geometryand material selection to provide a stable platform to catch debris andagainst which stage tool debris can be drilled. Also, the debris toolallows fragments to be drilled up into small enough pieces that can becirculated to surface without falling down hole or getting caughtbetween the drill string and the casing.

The debris barrier tool liner is formed of a material that providesadequate support, wherein the stage tool debris can be drilled andbroken up against seat 22 substantially before the seat itself is fullybroken down and drilled out. The material selection may be made toensure that the stage tool debris substantially cannot dig into ordestroy the liner 16, but the liner can be broken down by the drillingassembly. The stage tool stop and wiper plug may be formed of one ormore materials including, for example, cast iron, aluminum, rubber,polymers, etc. Barrier tool liner 16 may be formed of a material aboutthe same or harder than these materials, but still capable of beingdrilled out by standard tubing clean out drilling set ups, which meansit is softer than steel, the material from which casing 12 is made. Forexample, in one embodiment, the debris barrier tool liner 14 ismanufactured from cast iron, such as for example, ductile iron or grayiron, such as for example, class 30 to 50 gray iron, for example, class40 gray iron. Class 30 to 50 gray iron (i) is generally harder andstronger than the materials used in stage tool drillable components and(ii) is drillable and has a nodular grain structure, tending to crumbleinto small pieces when it is drilled out.

Ball 24 may be formed of various materials. In one embodiment, the ballis formed of a material the same as or softer than the liner, but isretained by seat 22 at the pressures employed. Ball 24 can wedge intoseat.

Housing 14 of tool 10 may be formed of steel or another material similarto the material from which casing 12 is made, which is harder than thematerial of liner 16.

FIG. 2C best shows the geometric features that enable liner 16 toprovide a stable platform for drilling out stage tool debris. Thesefeatures may also enable the seat to be drilled out without producingunnecessarily large fragments.

Tool 10 may include a contact shoulder between liner 16 and housing 14at a lower end of the liner that holds the liner in place against thecompressive load generated when the drill pushes down on the debris andthe seat. The contact shoulder is formed between an end wall 18 b ofrecess 18 and lower end 16 b of the liner. The end wall 18 b is abruptlyangled, such as at an acute or substantially right angle, at A betweenthe inner diameter of recess 18 and the end wall 18 b. This causes theend wall to form an annular platform that is planar or frustoconicallyformed. Liner 16 has a corresponding angled surface at its lower end 16b, which is for example, either planar or frustoconically formed withits thickness tapering toward the rear facing side. The correspondingshape of end 16 b and wall 18 b provides for good contact between theparts such that compressive force may be effectively transferred fromliner 16 to housing 14 and the liner tends to be driven into engagementwith housing rather than being driven inwardly into bore 14 c. Thus, thecontact shoulder provides a stable platform preventing the seat fromprematurely crumbling, even when sufficient weight is applied to thebarrier tool to drill out both the stage tool debris and the seat.

In addition, liner 16 has an outer diameter greater than the drilled outdiameter, which ensures that a cylindrical portion of the liner canremain after drill out. For example, liner 16 may have an outer diameter5 to 40% larger than the intended drilled out diameter (which depends onthe diameter of the mill). By placement in annular recess 18, thisenlarged outer diameter of liner 16 may be accommodated in the wall ofthe outer housing. For example, stated another way, liner 16 may have awall thickness at lower end 16 b that is substantially similar to thedepth of the annular recess at end wall 18 b. For example, the depth ofannular recess at end wall may be approximately 25 to 75% of thethickness of the wall of housing 14 and liner 16 thus has a thickness of25 to 75% of the thickness of the wall of housing 14, which causes theliner to have an outer diameter larger than the diameter of any mill tobe used to drill out the string. The thickness of the liner and itspositioning in recess beyond the reach of the mill ensures that aportion thereof resides in the annular recess and can remain thereineven after drill out. After drill out a cylindrical portion 16 s remainsin housing 14. Thus, the generation of large free fragments of the lineris avoided.

Liner 16 can have a similar enlarged outer diameter/minimum thicknessalong its length such that, for example, at upper end 16 a as well theliner can have a thickness approximately 25 to 75% of the thickness ofthe wall of housing 14. Upper end 16 a can, as well, be recessed inannular recess 18.

The tool's exposed bore 14 c, 20 has an initial length IL adjacentuphole end 14 a with a substantially constant inner diameter atsubstantially a full bore diameter, which is greater than the driftdiameter and generally greater than the drilled out diameter. The linerdefines at least portion of this initial length. In particular, bore 20at upper end 16 a of liner has an initial portion 20′ that extends alength at substantially the full bore diameter. At the lower end of thatinitial portion 20′, the inner walls at area 22 a of the liner definingbore 20 begin to taper towards the seat 22. The mill generally has adiameter less than full bore diameter. Thus, when the mill enters thetool, it will pass through the initial length IL, including initialportion 20′, at the upper end substantially without drilling into thebarrier tool. Instead, the mill will only start to actively contact,apply force against and drill out the liner where the walls taper to adiameter less than the diameter of the mill, which is large enough toform a suitable drilled out diameter that is often greater than or equalto drift diameter but less than the full bore diameter. Thus, contactwith the mill at the more fragile, upper end is avoided and the liner isdrilled out only further along its length where it is more fullysupported by liner material uphole and downhole of the contact region.This geometry acts against uncontrolled breakdown of the liner. Theinitial length IL having full bore diameter at the entrance to the lineralso guides the drilling assembly into the seat before drillingcommences.

The frustoconical surface 22 a also guides the drilling assembly intothe seat. In addition, the frustoconical surface 22 a ensures stage tooldebris 30 d that is pushed ahead of the drilling assembly can be packedtightly above ball 24 and is held in position to be acted upon bydrilling assembly 40, such that it can be drilled into small pieceswhile also drilling through the seat. Compression of debris 30 d aboveball 24 may also cause the debris to break down and be crushed betweendrilling assembly 40 and liner 16. By forming the liner of a materialwith a hardness and strength greater than that of the debris, it isensured that debris is supported by the liner, rather than digging intothe material of the liner.

In the illustrated embodiment, another interval in the bore of the toolat its lower end has a full bore diameter. Again, liner 16 defines atleast a portion, at 20″, of that interval, wherein bore 20 at lower end16 b of liner extends a length at substantially a full bore diameter. Assuch, again the lower end of the liner may have a large enough diametersuch that it is out of drilling contact with the mill during drill out.Thus, liner 16, which is more fragile at its ends, tends not to be actedupon (i.e. not drilled into) by the mill at portion 20′ and interval20″.

The liner has external threads 26 a on its rear facing side oppositeportion 20″ so that the tool can be threaded to the outer housing 14 ofthe debris barrier tool eliminating the opportunity for remnants of theseat to break off and fall down hole or become jammed. Threads 26 a mayextend from end 16 b up past portion 20″. Corresponding threads 26 b maybe formed in annular recess 18 and may extend fully to end wall 18 b.

The threads permit threaded engagement of the liner to the housing andprevent the seat from rotating during drill out. The threads may, forexample, be right handed to counteract the tendency to rotate impartedby operation of drilling assembly 40. During installation, liner 16 maybe threaded onto threads 26 b and torqued up to cause firm engagement ofliner 16 into housing 14. End wall 18 b may be formed by threadingtogether a lower portion and an upper portion of housing 14.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to those embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein, but is to beaccorded the full scope consistent with the claims, wherein reference toan element in the singular, such as by use of the article “a” or “an” isnot intended to mean “one and only one” unless specifically so stated,but rather “one or more”. All structural and functional equivalents tothe elements of the various embodiments described throughout thedisclosure that are known or later come to be known to those of ordinaryskill in the art are intended to be encompassed by the elements of theclaims. Moreover, nothing disclosed herein is intended to be dedicatedto the public regardless of whether such disclosure is explicitlyrecited in the claims. No claim element is to be construed under theprovisions of 35 USC 112, sixth paragraph, unless the element isexpressly recited using the phrase “means for” or “step for”.

1. A debris barrier tool comprising: a liner forming a seat in a borethrough the tool; and a ball formed to land in the seat, wherein theliner is formed of a cast iron.
 2. The debris barrier tool of claim 1wherein the liner is formed of class 30 to class 50 gray iron.
 3. Thedebris barrier tool of claim 1 further comprising an outer housingincluding an inner wall defining a bore and an annular recess in theinner wall and the liner being mounted in the annular recess and acontact shoulder formed between the outer housing and the liner at alower end of the liner.
 4. The debris barrier tool of claim 3 wherein alower end wall of the annular recess and a lower end of the liner arecorresponding shaped.
 5. The debris barrier tool of claim 3 wherein thetool has a drift diameter and the liner has an outer diameter greaterthan the drift diameter.
 6. The debris barrier tool of claim 2 whereinthe outer housing is formed of a material harder than cast iron.
 7. Thedebris barrier tool of claim 1 further comprising a full bore diameterportion between an upper end of the liner and the seat.
 8. The debrisbarrier tool of claim 7 further comprising a frustoconical surfacebetween the upper end and the seat.
 9. The debris barrier tool of claim1 further comprising a full bore diameter interval at a lower end of theliner.
 10. The debris barrier tool of claim 9 further comprising anouter housing and the liner is mounted within the outer housing andthreadedly engaged to the outer housing opposite the full bore diameterinterval.
 11. The debris barrier tool of claim 1 further comprising aright hand thread between the seat and the outer housing preventingrotation of the seat during drill out.
 12. A method for drilling out awellbore string comprising: landing a ball in a seat of a debris barriertool; operating a drilling assembly to drill through the wellbore stringuphole of the debris barrier tool; and drilling through the seat of thedebris barrier tool while debris from uphole drilling is crushed betweenthe drilling assembly and the debris barrier tool.
 13. The method ofclaim 12 wherein drilling through the seat includes passing the drillingassembly through a full bore portion at an upper end of a drillableliner on which the seat is formed without drilling into the full boreportion.
 14. The method of claim 12 wherein drilling the debris barriertool includes passing the drilling assembly through a full bore intervalat a lower end of the drillable liner without drilling into the fullbore interval.
 15. The method of claim 12 wherein drilling through theseat leaves a cylindrical portion of the seat remaining in debrisbarrier tool.
 16. The method of claim 12 wherein during drilling,stopping rotation of the seat by providing a thread engaging the seat toan outer housing of the debris barrier tool.
 17. The method of claim 12further comprising circulating fluid through the drilling assembly. 18.The method of claim 12 further comprising stage cementing through astage tool uphole of the debris barrier tool and operating a drillingassembly drills out portions of the stage tool.